Fixup pusher pool notifications (#8287)

`pusher_pool.on_new_notifications` expected a min and max stream ID, however that was not what we were passing in. Instead, let's just pass it the current max stream ID and have it track the last stream ID it got passed.

I believe that it mostly worked as we called the function for every event. However, it would break for events that got persisted out of order, i.e, that were persisted but the max stream ID wasn't incremented as not all preceding events had finished persisting, and push for that event would be delayed until another event got pushed to the effected users.

8 files changed, 24 insertions, 8 deletions

diff --git a/changelog.d/8287.bugfix b/changelog.d/8287.bugfix
new file mode 100644
index 0000000000..839781aa07
--- /dev/null
+++ b/changelog.d/8287.bugfix
@@ -0,0 +1 @@
+Fix edge case where push could get delayed for a user until a later event was pushed.
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 43f2986f89..74d7ac8a67 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -2970,7 +2970,7 @@ class FederationHandler(BaseHandler):
             event, event_stream_id, max_stream_id, extra_users=extra_users
         )
 
-        await self.pusher_pool.on_new_notifications(event_stream_id, max_stream_id)
+        await self.pusher_pool.on_new_notifications(max_stream_id)
 
     async def _clean_room_for_join(self, room_id: str) -> None:
         """Called to clean up any data in DB for a given room, ready for the
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 8a7b4916cd..d1556659e3 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -1145,7 +1145,7 @@ class EventCreationHandler:
             # If there's an expiry timestamp on the event, schedule its expiry.
             self._message_handler.maybe_schedule_expiry(event)
 
-        await self.pusher_pool.on_new_notifications(event_stream_id, max_stream_id)
+        await self.pusher_pool.on_new_notifications(max_stream_id)
 
         def _notify():
             try:
diff --git a/synapse/push/emailpusher.py b/synapse/push/emailpusher.py
index b7ea4438e0..28bd8ab748 100644
--- a/synapse/push/emailpusher.py
+++ b/synapse/push/emailpusher.py
@@ -91,7 +91,7 @@ class EmailPusher:
                 pass
             self.timed_call = None
 
-    def on_new_notifications(self, min_stream_ordering, max_stream_ordering):
+    def on_new_notifications(self, max_stream_ordering):
         if self.max_stream_ordering:
             self.max_stream_ordering = max(
                 max_stream_ordering, self.max_stream_ordering
diff --git a/synapse/push/httppusher.py b/synapse/push/httppusher.py
index f21fa9b659..26706bf3e1 100644
--- a/synapse/push/httppusher.py
+++ b/synapse/push/httppusher.py
@@ -114,7 +114,7 @@ class HttpPusher:
         if should_check_for_notifs:
             self._start_processing()
 
-    def on_new_notifications(self, min_stream_ordering, max_stream_ordering):
+    def on_new_notifications(self, max_stream_ordering):
         self.max_stream_ordering = max(
             max_stream_ordering, self.max_stream_ordering or 0
         )
diff --git a/synapse/push/pusherpool.py b/synapse/push/pusherpool.py
index 3c3262a88c..fa8473bf8d 100644
--- a/synapse/push/pusherpool.py
+++ b/synapse/push/pusherpool.py
@@ -64,6 +64,12 @@ class PusherPool:
         self._pusher_shard_config = hs.config.push.pusher_shard_config
         self._instance_name = hs.get_instance_name()
 
+        # Record the last stream ID that we were poked about so we can get
+        # changes since then. We set this to the current max stream ID on
+        # startup as every individual pusher will have checked for changes on
+        # startup.
+        self._last_room_stream_id_seen = self.store.get_room_max_stream_ordering()
+
         # map from user id to app_id:pushkey to pusher
         self.pushers = {}  # type: Dict[str, Dict[str, Union[HttpPusher, EmailPusher]]]
 
@@ -178,20 +184,27 @@ class PusherPool:
                 )
                 await self.remove_pusher(p["app_id"], p["pushkey"], p["user_name"])
 
-    async def on_new_notifications(self, min_stream_id, max_stream_id):
+    async def on_new_notifications(self, max_stream_id):
         if not self.pushers:
             # nothing to do here.
             return
 
+        if max_stream_id < self._last_room_stream_id_seen:
+            # Nothing to do
+            return
+
+        prev_stream_id = self._last_room_stream_id_seen
+        self._last_room_stream_id_seen = max_stream_id
+
         try:
             users_affected = await self.store.get_push_action_users_in_range(
-                min_stream_id, max_stream_id
+                prev_stream_id, max_stream_id
             )
 
             for u in users_affected:
                 if u in self.pushers:
                     for p in self.pushers[u].values():
-                        p.on_new_notifications(min_stream_id, max_stream_id)
+                        p.on_new_notifications(max_stream_id)
 
         except Exception:
             logger.exception("Exception in pusher on_new_notifications")
diff --git a/synapse/replication/tcp/client.py b/synapse/replication/tcp/client.py
index d6ecf5b327..ccd3147dfd 100644
--- a/synapse/replication/tcp/client.py
+++ b/synapse/replication/tcp/client.py
@@ -154,7 +154,8 @@ class ReplicationDataHandler:
                 max_token = self.store.get_room_max_stream_ordering()
                 self.notifier.on_new_room_event(event, token, max_token, extra_users)
 
-            await self.pusher_pool.on_new_notifications(token, token)
+            max_token = self.store.get_room_max_stream_ordering()
+            await self.pusher_pool.on_new_notifications(max_token)
 
         # Notify any waiting deferreds. The list is ordered by position so we
         # just iterate through the list until we reach a position that is
diff --git a/tests/handlers/test_typing.py b/tests/handlers/test_typing.py
index ae6bc24f4c..f306a09bfa 100644
--- a/tests/handlers/test_typing.py
+++ b/tests/handlers/test_typing.py
@@ -80,6 +80,7 @@ class TypingNotificationsTestCase(unittest.HomeserverTestCase):
                 "get_user_directory_stream_pos",
                 "get_current_state_deltas",
                 "get_device_updates_by_remote",
+                "get_room_max_stream_ordering",
             ]
         )